Specific designs for landfill liner systems will vary depending on the specific local geology and state and local regulatory requirements. However, common elements in such systems, from the lowermost elements upward, may include (1) a lower compacted clay liner that lies above undisturbed in situ soils, (2) one or more lower high-density polyethylene (HPDE) liners, (3) one or more lower drainage layers, (4) one or more intermediate HPDE liners, (5) intermediate cushion and drainage layers, (6) compacted waste lifts with daily cover soil between lifts (7) an upper cushion layer (8) an HPDE cap liner (9) an upper drainage layer (10) a soil barrier layer (11) topsoil, and (12) vegetative cover.
In addition to these layered elements, the landfill will include a leachate collection system including a network of leachate collection pipes, a leachate sump, one or more leachate pumps, and a leachate collection container/reservoir. Groundwater monitoring wells are installed to monitor the presence of contaminants around the landfill site that may seep into the underlying groundwater zone if there is a failure or breach of system.
Gas monitoring probes are also installed to monitor the presence of gases produced from waste decomposition such as methane. Landfill gas collection is also a requirement and landfill gas collection is typically achieved through use of gas wells installed in the waste mass. Gas header manifolds communicate with the wells to capture and transport the waste gas for treatment or disposal, such as at a local flare plant or a landfill gas to energy (LFGTE) plant.
As one should appreciate from the foregoing, there are extensive design requirements for municipal solid waste facilities. There are many regulatory design requirements and corresponding literature that describes existing landfill designs since these designs are subject to considerable local, state, and federal regulations.
Although landfill design includes a many technological solutions, one noteworthy deficiency in landfill design is the inability to reliably and economically provide a liner system for municipal waste facilities that have near vertical or vertical walls.
Environmental regulations in the United States and many other countries require liners for solid waste facilities to have specified hydraulic properties to withstand forces produced on the liners as operation of a facility progresses over time. One category of landfills in the U.S. is referred to as “subtitle D” landfills. These landfills, by regulation, are required to incorporate a 2-ft thick compacted clay liner (CCL) that has a permeability less than or equal to 1.0×10−7 cm/s. In a more extreme case, landfills operated in converted rock quarries are required to install a 10-foot thick CCL along the side walls of the facility. If the facility does not have the liner material, it must be imported. The requirement to import liner material is very costly to the landfill operation. The equipment and manpower necessary to install a CCL is significant; thus adding additional cost to the landfill operation. Use of a 10-foot thick liner also reduces the available volume of the facility to hold waste thus reducing revenue for the facility by limiting its capacity.
There are alternative liners used in waste containment facilities to reduce the constraints of a CCL. For example, a commonly used alternate liner is a geo-synthetic clay liner (GCL) which is a much thinner woven geo-synthetic material with an imbedded barrier layer (e.g. bentonite). The imbedded layer expands or swells when exposed to moisture, and this expansion provides the non-permeable barrier required for some landfill designs.
While GCL is an alternative barrier liner solution, GCL also has clear shortcomings. GCL is susceptible to damage by equipment used to operate the facility because it can be punctured and torn. GCL may have sufficient shear strength to prevent tearing when installed on an undisturbed horizontal surface, but heavy equipment can damage the GCL and it can be difficult to determine when damage occurs because of soil and rock that may partially cover the GCL as it is installed. Another disadvantage of GCL is that it cannot be installed on near vertical slopes. Solid waste in a landfill facility will experience significant settlement as the waste decomposes. The waste adheres to the GCL and can subsequently puncture or tear the GCL. If the imbedded barrier layer in the GCL is installed on a near vertical surface, the GCL may also settle resulting in the upper portion of a sheet of GCL being thinner than the lower portion. Subsequently the thinned upper portion may not have the required barrier thickness.
Other methods of lining vertical walls of a landfill include the use of precast concrete structures built along the side walls of the facility. Intact concrete is essentially an impermeable material. However concrete can develop cracks for a multitude of reasons rendering use of concrete by itself a non-viable alternative liner system. If the concrete is exposed to moisture, freeze-thaw cycles can cause cracking even in the highest quality concrete. Precast concrete panels are expensive not only for the material costs, but also transportation costs since most landfills do not have a precast concrete manufacturing facility.
Another method for lining vertical walls of a landfill includes the use of rubber membranes that may prevent potentially harmful liquids (leachate) from entering cracks in an underlying barrier material. However, as mentioned, solid waste will experience settlement as the waste decomposes. The waste can adhere to the rubber liner and as the waste settles. Down drag forces caused by the shifting waste can also create tears in a rubber membrane thereby compromising the integrity of the landfill facility.
Considering the shortcomings of the prior art, there is a need to provide a barrier liner design that can handle drag down forces created by waste decomposition. There is also a need to provide a barrier liner design that can better withstand damage produced by heavy equipment or other external forces. There is yet further a need to provide a barrier liner design that is cost effective and complies with regulatory requirements.